1. Field of the Invention
The present invention relates to a rotor coupling having insulated structure that is preferably employed in power generating equipment in which a generator is disposed in between a steam turbine and a gas turbine or a rotating machinery such as another steam turbine. More specifically, the present invention relates to a rotor coupling having insulated structure that is designed to stop galvanic corrosion of the rotor, bearing members and the like which occurs due to the generation of shaft voltage.
2. Description of the Related Art
An example of conventional power generating equipment will be explained with reference to FIG. 8. In this figure, 1 is a steam turbine, 2 is a generator, and 3 is a gas turbine or a rotating machinery such as another steam turbine (the following explanation employs a gas turbine as an example of this rotating machinery, however the same explanation applies to the case where another steam turbine is employed in place of the gas turbine). A rotor 1a of the steam turbine 1 and a rotor 2a of the generator 2 are connected to the same shaft via a clutch 5. The rotor 2a of the generator 2 and a rotor 3a of the gas turbine 3 are also connected to the same shaft by a rotor coupling 6. In addition, each rotor 1a, 2a, 3a is supported by bearing members 7 in a manner so as to permit rotation.
By employing a design in which the generator 2 is disposed in between the steam turbine 1 and gas turbine 3 in this way, it is possible to disengage between the steam turbine 1 and gas turbine 3. As a result, the stream turbine 1 and gas turbine 3 can be disengaged using the clutch 5, as compared to a design in which the generator, steam turbine, and gas turbine (or the rotating machinery such as another steam turbine) are disposed in sequence. Thus, greater flexibility in operation can be achieved.
In the arrangement shown in FIG. 8, the shaft voltage is theoretically different between the shaft on the driver side and the opposite side of the generator 2. For this reason, when these are linked (via a grounded earth grid, for example), a large amount of current flows to each of the rotors 2a, 1a, 3a in this loop.
When the shaft voltage of this sort exceeds a limit value, the insulation between the rotors 1a, 3a and each bearing member 7 is disrupted, allowing discharge to occur. As a result, journals and outer surface of ground devices of the rotors 1a, 3a and bearings of the bearing members 7 are damaged by the effects of galvanic corrosion.
As shown in FIG. 8, a preventative measure for this type of damage calls for releasing shaft current by providing a grounding electrode 9a in between the steam turbine 1 and generator 2.
Normally, by grounding one point in a continuous conductor like each rotors 1a, 2a, 3a, it is possible to achieve the same potential at all sites. However, in a shaft system having a design in which the generator 2 is disposed in between the steam turbine 1 and gas turbine 3, even if one point of the rotor 1a, 2a, 3a is grounded, the potential at a point away from this grounded point can be high. Accordingly, simply employing a grounding electrode 9a has not been a sufficient countermeasure.
Therefore, a strategy was investigated for preventing the potential at the rotor 3a, which is away from the grounding electrode 9a, from becoming high by providing another grounding electrode 9b in between the gas turbine 3 and generator 2 as shown in FIG. 8. However, when two grounding points are employed in this way, a large amount of circular loop current (mainly an alternating current component generated at the generator 2) circulates as shown by arrow c in the figure if separate earth grids are not provided (if two grounding points are connected, for example), and the current gives to damage to the rotors 1a, 3a and bearing members 7 from the effects of galvanic corrosion due to the shaft voltage as explained above.
Accordingly, grounding electrodes 9a, 9b alone were not a sufficient countermeasure to the shaft voltage, so that a new approach has been greatly desired.